A phase-changeable memory device is a kind of non-volatile memory device. Phase-changeable memory devices may use a phase-changeable material such as a chalcogenide compound that can be switched between a crystalline state and an amorphous state based on applied electrical signals, thereby exhibiting a high-resistance state and a low-resistance state that can be distinguished from each other. In response to applied voltages, current flow through the phase-changeable material may heat the phase-changeable material. Depending on the heating temperature and duration, the phase-changeable material may be changed to a program state of a high-resistance (i.e., a reset state) or a low-resistance (i.e., a set state). The high-resistance state and the low-resistance state may be switched and/or reversed based on the applied current.
The heating temperature of the phase-changeable material may be proportional to the amount of applied current. In order to achieve a relatively high density of integration, it may be desirable to reduce the temperature by reducing a program current flow. More particularly, it may be desirable to reduce the switching current for the reset state, as switching to the reset state may require more current than switching to the set state.